Electroplating operations are often used in many industrial applications, such as for plating thin film wiring onto ceramic substrates to manufacture integrated circuits for the semiconductor industry. FIGS. 1 and 2 show a side view and a top view, respectively, illustrating a typical electroplating apparatus 100 used in such manufacture. Plating tank 101 contains an acid bath of electroplating solution that generally comprises metal ions in an acid solution.
Plating tank 101 may be separated into two isolated compartments 12 and 14 by a divider 16. Each compartment 12, 14 is outfitted for an independent electroplating operation. One or more plating fixtures 18, each containing a substrate 19 to be plated, is or are attached to a substrate carrier such as flybar 20. Flybar 20 is moved by a robot (not shown) that grabs flybar 20 at robot interface 22. Flybar 20 is lowered vertically in the direction of arrow "A" into plating tank 101.
When flybar 20 has been fully lowered into a plating position where plating fixtures 18 are submerged inside plating tank 101, fixed contact blocks 24 on opposite ends of flybar 20 become aligned with movable contact mechanisms 26 attached externally to plating tank 101. Fixed contact block 24 and movable contact mechanism 26 adjacent plating tank compartment 12 provide an independent electrical contact mechanism for compartment 12 that is isolated from the equivalent, mirror-image components related to and adjacent compartment 14.
Referring now to FIGS. 3 and 4, there are shown enlarged illustrations of a top and side view, respectively, of movable contact mechanism 26. Movable contact mechanism 26 essentially comprises a frame 30, to which is attached a piston or air plunger 32 that is linked by linkage 33 to movable contact block 34. Rollers 35 may be present if any horizontal motion of flybar 20 is necessary after it comes to rest on frame 30. Fixed contact block 24, as shown in FIGS. 1 and 2, and movable contact block 34 each further comprise a set of fixed contacts 36 and 36' and 37 and 37', respectively. Each contact 36, 36', 37, and 37' may merely comprise the protruding threaded end of a screw 38 threaded through respective contact block 24 or 34.
When contact blocks 24 and 34 are aligned, movable contact mechanism 26 is activated. Piston 32 retracts so that linkage 33 pivots about pin 40, thus moving contact block 34 toward fixed contact block 24 along the direction of arrow "B" to reach the closed position as shown in FIGS. 3 and 4. When the electroplating operation is finished, piston 32 extends so that linkage 33 pivots about pin 40 in opposite direction, thus moving contact block 34 in the direction opposite arrow "B" to an open position (not shown).
In the closed position, contacts 36 and 36' touch contacts 37 and 37' respectively and electrical current flows from independent power supplies (not shown) connected one each to contacts 37 and 37'. The power supply attached to contact 37 is generally at a different potential than the power supply attached to contact 37'.
Thus, a first current having a first potential flows through contact 37 into contact 36 and a second current having a second potential flows through contact 37' into contact 36'. Both currents flow through independent electrical connections (not shown) across flybar 20 to the plating fixtures 18, where one current is attached to the substrate 19 and one is attached to the "thief" 21, shown in FIG. 1. Thus, the cathode potentials of the substrate 19 and thief 21 interact with each other and with an anode (not shown) submerged in the electroplating solution to uniformly attract and adhere metal ions from the solution to the substrate 19. The differing potentials of substrate 19 and thief 21 interact to eliminate the edge effect, excess plating on the edges as compared to the center of the substrate 19, as is well-known in the art.
Because of the acidic, corrosive atmosphere created by the highly acidic electroplating solution, contacts 36, 36' and, in particular, 37, 37' may corrode. The corroded contacts may produce non-conductive corrosion byproducts, over time, that build-up upon the mating surface of contacts 36, 36' and 37, 37'. Thus, after some period of time, the electrical contact provided between contacts 36, 36' and 37, 37' may deteriorate and become intermittent. A poor or intermittent electrical connection may lead to incomplete plating of the conductive metal onto the substrate 19. These incompletely plated substrates may then be classified as unrecoverable scrap.
Therefore, there is a need for electroplating apparatus having electrical contacts that overcome the problems caused by corrosion in the hostile electroplating environment.